JP2845231B2 - Variable length encoding method and apparatus therefor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a variable length coding method and apparatus, and more particularly to a variable length coding method and apparatus suitable for recording and transmitting moving picture signals.

[0002]

2. Description of the Related Art Conventionally, MPEG (moving picture coding experts group) has been used as information compression means used for recording or transmitting moving image signals to storage media.
p) method is used. In MPEG, orthogonal transform is used in information source coding to reduce the frequency redundancy of a moving image signal. Further, two-dimensional variable length coding is performed by combining a run indicating the number of consecutive invalid data and an amplitude value of valid data appearing next to the consecutive invalid data as a level and combining the run and the level.

[0003] Two-dimensional variable length coding is shown in FIG.
As shown in (1), short variable-length codes are assigned to data having a short run and a small amplitude value and a high frequency of occurrence. In addition,
Table 1 lists data having a high frequency of occurrence and data having a low frequency of occurrence with respect to an example of correspondence between runs, levels, codes, and code lengths.

[0004]

[Table 1]

Referring to Table 1, for example, when the run is 0 and the amplitude (level) is 1, a 3-bit code is assigned, and when the run is 1 and the level is 31, a 17-bit code is assigned. ing. On the other hand, in the case of data having a long run and a large amplitude value and a low occurrence frequency, for example, run 0 level 41, a 24-bit long code is assigned.

[0006]

When recording a moving image signal on a recording medium such as an optical disk, a video tape, or a hard disk, the recording capacity is limited. Therefore, the moving image signal is compression-coded and recorded. Also, in the transmission of a moving image signal using a transmission path, the moving image signal is compression-encoded and transmitted due to the limitation of the capacity of the transmission path. Then, as described above, the compression encoding of the moving image signal is performed by MP.
An EG method or the like is used.

By the way, in the case of compression coding for broadcast business use, the amount of information for each frame is fixed so that editing on a frame basis is possible. However, it is very difficult to control the amount of information per frame to a predetermined value.

In the conventional information source coding and variable length coding method, for example, the upper half of the screen is a flat pattern, and the lower half is a fine pattern such as CG (computer graphics) which is often used recently. In the first case (upper half of the screen), the pattern is flat, so the total number of variable length codes generated is small. Many long and large levels of data will be generated.

As a result, a large number of codes having a long code length are generated, and the amount of generated information sharply increases, so that the amount of information exceeds a predetermined amount of information. Unable to send data to.

[0010] When the encoded data recorded in such a situation is read out from the recording medium and decoded, there occurs a phenomenon that the lower portion of the screen cannot be decoded and the image is cut off. Will do. Similarly, in moving image transmission using a transmission path, a screen break has occurred.

Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to record a moving image signal on a recording medium or send it to a transmission line by using a long variable length code. It is an object of the present invention to provide a variable-length encoding method and apparatus capable of avoiding unrecorded data on a recording medium or non-transmission of data to a transmission line even when the error occurs.

[0012]

In order to achieve the above object, a variable length coding method according to the present invention uses a plurality of screens when compressing a moving image signal by combining information source coding and variable length coding. By dividing the image into blocks of pixels, performing orthogonal transformation and quantization, the frequency redundancy of the moving image signal is reduced, and further scanning within the block is performed in a predetermined direction. When a variable length code having a short code length is assigned to data with a high frequency of occurrence when variable length encoding is performed by combining the amplitude value of valid data appearing next to the indicated run and invalid data as one code. In variable length coding in which a variable length code having a long code is assigned to data having a low length, the number of predetermined long codes to be generated is counted, and variable according to the number of long codes. Comprising means for switching the processing method of the variable-length code generated by the encoding.

Further, according to the variable length coding method of the present invention, when compressing a moving image signal by combining information source coding and variable length coding, a screen is divided into blocks each having a plurality of pixels, and orthogonal transform and orthogonal transform are performed. By performing the quantization, the frequency redundancy of the moving image signal is reduced, and furthermore, the block is scanned in a predetermined direction, and the run represented by the continuous number of invalid data and the next data appear next to the invalid data. When variable-length coding is performed by combining the amplitude values of valid data as one code, a variable-length code having a short code length is assigned to data with a high frequency of occurrence, and a code with a long code length is allocated to data with a low frequency of occurrence. In variable-length coding for allocating variable-length codes, the number of predetermined long codes to be generated is counted, and the quantization parameter in information source coding is determined according to the number of long codes. And means for instructing the switching of over data.

In the variable length coding method according to the present invention, the number of predetermined long codes generated by the variable length coding is counted in units of a block composed of a plurality of pixels, and the counted number of long codes is counted. When the value becomes equal to or more than a predetermined value n, the variable length code in the subsequent blocks is replaced with zero to perform variable length coding.

Further, in the variable length coding method according to the present invention, the number of predetermined long codes continuously generated by the variable length coding is counted in units of blocks composed of a plurality of pixels, and the continuous long codes are counted. When the number becomes equal to or greater than a predetermined value n, the variable length code in the subsequent blocks is replaced with zero to perform variable length coding.

Still further, in the variable length coding method according to the present invention, the number of predetermined long codes generated by the variable length coding is counted in units of a block composed of a plurality of pixels, and the counted long codes are counted. When the number is equal to or larger than a predetermined value n, a means for issuing an instruction to coarsen the quantization parameter in the predetermined period information source coding is provided.

In the variable length coding method according to the present invention, the number of predetermined long codes continuously generated by the variable length coding is counted in units of blocks composed of a plurality of pixels, and the continuous long codes are counted. Means for issuing an instruction to coarsen the quantization parameter in the predetermined period information source coding when the number becomes equal to or greater than a predetermined value n.

The variable length coding apparatus according to the present invention is a variable length coding circuit which blocks an input image signal into units of a predetermined number of pixels, orthogonally transforms the blocks, and quantizes the data to perform variable length coding. A means for counting long codes generated in a block, and when the counted value exceeds a predetermined number, switching means for changing a variable length code in the block thereafter to an invalid value; It is characterized in that occurrence is prevented.

Further, the variable-length coding apparatus of the present invention performs variable-length coding on data from an information source coding unit which blocks an input image signal into a predetermined number of pixels, orthogonally transforms the blocks, and further quantizes the blocks. In the variable length encoding circuit, when the long code generated in the block is counted and the counted value exceeds a predetermined number, the quantization in the information source coding unit is performed for a predetermined period for a predetermined period. It is characterized in that roughing is instructed to prevent generation of excessive information.

[0020]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention. Referring to FIG. 1, a variable length encoder includes an information source encoding unit 1 that receives a moving image signal as input, and a variable length encoder 2 that receives an output of the information source encoding unit 1 and outputs a variable length code. 2
Has a variable length encoding unit 21 and an escape counter 22.

In the information source coding unit 1, the frequency redundancy of the input video signal is reduced by using an orthogonal transform or the like.

The data whose frequency redundancy has been reduced by the information source coding unit 1 is sent from the line 101 to the variable length coding unit 21 of the variable length coder 2 where variable length coding is performed. .

Further, the information source coding unit 1 supplies a block synchronization signal indicating a block break to the escape counter 22 of the variable length coder 2 from a line 102.

The variable length code generated by the variable length coding unit 21 changes according to the picture of the input moving image signal. In a general example, a short symbol is assigned to a flat pattern because the frequency of occurrence is high. In addition, since the appearance probability of an image having a fine pattern and including a high frequency component is generally low, a long code is assigned.

Then, the variable-length encoding unit 21 sends an escape signal 211 to the escape counter 22 when data having a low frequency of occurrence shown in FIG.

The escape counter 22 counts the number of long codes (24-bit codes) having a low occurrence frequency indicated by the escape signal 211 with reference to the input block synchronization signal. For example, when counting the number of codes having a low occurrence frequency in block units, the escape counter 22 is reset by a block synchronization signal, and every time a long code is generated and the escape signal 211 is given to the escape counter 22, the escape counter 22 is reset. Updates the count value (counts up).

In this way, when the count value of the escape counter 22 becomes equal to or more than the predetermined value n, the escape counter 22 supplies the encoding stop signal 213 to the variable length encoding unit 21. Then, when the next block synchronization signal is provided from the information source coding unit 1, the escape counter 22 is reset and the coding stop signal 213 is released.

The variable length encoding unit 21 outputs an encoding stop signal 2
While 13 is given, the generation of the variable length code 201 is stopped, and the encoded information is reduced.

As a method of stopping encoding when a code having a low frequency of occurrence continues in a block for a predetermined number or more, the escape counter 22 outputs the escape signal 211 from the variable length encoding unit 21 continuously. The count value is updated, and the escape signal 211
Is reset, the count value is reset (to zero). When the count value becomes equal to or more than a predetermined value n, the escape counter 22 outputs the encoding stop signal 213 to the variable length encoding unit 2 until the next block.
Give to 1.

Next, a second embodiment of the present invention will be described with reference to FIG. Referring to FIG. 2, in this embodiment, information source coding section 1 reduces the frequency redundancy of an input video signal using orthogonal transform or the like.

The data whose redundancy has been reduced in frequency by the information source coding unit 1 is sent from a line 101 to a variable length coding unit 21 of a variable length coding unit 2, where variable length coding is performed.

Further, the information source encoding unit 1 supplies a block synchronization signal indicating a block delimiter to an escape counter 22 included in the variable length encoder 2 via a line 102.

The variable length coding unit 21 is provided in accordance with FIG.
When the data having a low frequency of occurrence is given, an escape signal 211 is sent to the escape counter 22. The escape counter 22 counts the number of long codes (24-bit codes) having a low occurrence frequency indicated by the escape signal 211 with reference to the input block synchronization signal. For example, when counting the number of infrequently occurring codes in block units, the escape counter 22 is reset with a block synchronization signal, and every time a long code is generated and the escape signal 211 is given to the escape counter 22,
The escape counter 22 updates the count value.

When the count value becomes equal to or greater than a predetermined value n, the escape counter 22 outputs, as the encoding control information 214, control information for coarsening information source encoding parameters such as quantization to the information source. This is given to the encoding unit 1.

According to the coding control information 214 input from the escape counter 22, the information source coding unit 1 coarsens the coding parameters to reduce the amount of coding information.

When counting only the continuous escape signal 211, when the escape signal 211 is released, the escape counter 22 resets the count value. When the value of the counter becomes equal to or more than a predetermined value n by counting the continuous escape signals 211, the escape counter 22 holds the value until the next reset signal is given.

As the coding control information 214, control information for coarsening the parameters of the information source coding such as quantization is given to the information source coding unit 1 for a predetermined time (period).

The information source coding unit 1 coarsens the coding parameters according to the coding control information 214 given from the escape counter 22 to reduce the amount of coding information.

[0039]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention;

The basic configuration of one embodiment of the present invention is the same as the configuration shown in FIG. 1 referred to in the description of the above embodiment. Referring to FIG. 1, in the present embodiment, the escape counter 22 of the variable length encoder 22 counts the number of escape signals 211 in a block, and when the counted value becomes equal to or larger than a predetermined value, the variable length The encoding is stopped to reduce the amount of encoded information. The input moving image signal is supplied to the information source coding unit 1.

FIG. 3 shows details of the configuration of the information source coding unit 1 as an embodiment of the present invention. Referring to FIG. 3, the information source coding unit 1 includes a blocking circuit 100, an orthogonal transformer 110, and a quantizer 120.

The input moving picture signal supplied to the information source coding unit 1 is divided into blocks each having a predetermined number of pixels in a blocking circuit 100. Further, the blocking circuit 100 outputs a block synchronization signal indicating a block break.

The moving picture signal divided into blocks by the blocking circuit 100 is sent to the orthogonal transformer 100 and subjected to orthogonal transform, so that the frequency redundancy of the input moving picture signal is reduced. Then, the moving image signal orthogonally transformed by the orthogonal transformer 110 is sent to the quantizer 120 and quantized. The coded data quantized by the quantizer 120 is supplied to the variable length coding unit 21 of the variable length coder 2 shown in FIG.

The block synchronization signal output from the blocking circuit 100 is supplied to the escape counter 22 of the variable length encoder 2 shown in FIG.

FIG. 4 is a diagram showing the details of the configuration of the variable length encoder 2 in one embodiment of the present invention.

Referring to FIG. 4, the variable length encoder includes a variable length coding unit 21 and an escape counter 22. The variable length coding unit 21 includes a code table for generating a variable length code. 210, a switch 240 for stopping variable-length coding, and a barrel shifter 250 for packing variable-length codes.

The coded data supplied from the information source coding unit 1 via the line 101 is supplied to the code table 210 of the variable length coding unit 21.

The code table 210 statistically examines the probability of occurrence of coded data whose frequency redundancy has been reduced by orthogonal transformation or the like based on various kinds of moving picture signals, and converts the probability of occurrence into coded data having a high occurrence frequency. Assigns a short code and assigns a long code to encoded data with a low frequency of occurrence, for example, to prepare and prepare in advance a variable-length code conversion table as shown in Table 1 above.

When the moving image data is converted into a variable-length code, as shown in Table 1 above, when the moving image data is converted into a long code having a low frequency of occurrence, as shown in FIG. "1" is output as a signal (the escape signal 211 is activated). FIG. 5 is a diagram for explaining the operation of one embodiment of the present invention.

The variable length code generated by code table 210 is supplied to switch 240 via line 2124.

The escape signal generated by the code table 210 is supplied to the escape counter 22 via a line 211.

As shown in FIG. 5, the escape counter 22 updates the value of the counter when the escape signal is "1" and holds the value of the counter when the escape signal is "0". When the value of the counter exceeds a predetermined value n, an encoding stop signal is generated.

Further, the escape counter 22 resets the value of the counter to zero at the beginning of the block by the block synchronization signal supplied from the information source coding unit 1 via the line 102.

The encoding stop signal generated by the escape counter 22 is supplied to the switch 240 via the line 213.

The switch 240 changes the variable length code supplied from the code table 210 via the line 2124 to the line 240.
An invalid code given via 0, for example, a code having an amplitude value of zero, is switched according to a coding stop signal supplied via a line 213 from the escape counter 22.

When the coding stop signal is "1", the coding is not stopped. When the coding stop signal is "0", the coding is stopped.

As shown in FIG. 5, when the encoding stop signal supplied from the escape counter 22 via the line 213 is “1”, indicating that the encoding is to be performed, the switch 240 The variable length code supplied from the table 210 via the line 2124 is selected and output from the switch 240.

When the encoding stop signal supplied from the escape counter 22 via the line 213 is set to "0" to indicate that the encoding has been stopped, the switch 240
400 to select the invalid code supplied via
The output is 40.

The variable length code output from the switch 240 is supplied to a barrel shifter 250 via a line 2425.

The barrel shifter 250 packs the variable length code supplied from the switch 240 via the line 2425. Since the variable-length code supplied from the switch 240 has various code lengths, the variable-length code is packed in, for example, 8-bit units by a barrel shifter to eliminate waste when writing to a recording medium or transmitting to a transmission path. I do.

Next, as another method (modification) in the above-described embodiment, continuous escape signals in a block are counted, and when the counted value is equal to or larger than a predetermined value n, encoding is stopped. The method will be described.

In this method, the operations of the code table 210, the switch 240 and the barrel shifter 250 of the variable length coding unit 2 shown in FIG. This is similar to the method of the above-described embodiment in which the encoding is stopped when the value becomes equal to or greater than a predetermined value n.

In this method, only the operation of the escape counter 22 is different from that of the above embodiment. Therefore, only the operation of the escape counter 22 will be described below.

Referring to FIG. 4, escape counter 22
Is reset to zero at the beginning of a block by a block synchronization signal provided via line 102. Then, the escape signal supplied from the code table 210 via the line 211 is counted. In counting the escape signals, only the continuous escape signals are counted, as shown in FIG. FIG. 6 is a diagram for explaining the operation of a modification of the embodiment of the present invention.

That is, referring to FIG. 6, when the escape signal becomes "1" or "0", the value of escape counter 22 is reset to zero (zero).

For this reason, when the escape signal continues for a predetermined value n or more, the escape counter 22 outputs a coding stop signal.

Next, a second embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. Referring to FIG. 2, a second embodiment of the present invention is shown.
Is an escape counter 22 of the variable length encoder 2.
Counts the number of escape signals indicating that a long code in a block has been generated, and, when the counted value is equal to or greater than a predetermined value n, encodes coding control information for performing coarse quantization into an information source code. A predetermined time is given to the encoding unit 1 to reduce the amount of encoded information. The input moving image signal is supplied to the information source coding unit 1.

FIG. 7 shows the configuration of the information source coding unit 1 according to the second embodiment of the present invention.

Referring to FIG. 7, the information source encoding unit 1
It comprises a blocking circuit 100, an orthogonal transformer 110, and a quantizer 120. Blocking circuit 1
00 divides an input moving image signal into blocks each having a predetermined number of pixels. At the same time, a block synchronizing signal indicating a block break is generated.

The moving image signal divided into blocks is orthogonally transformed by the orthogonal transformer 110 to reduce the frequency redundancy. The encoded data orthogonally transformed by the orthogonal transformer 110 is quantized by the quantizer 120, and the redundancy of the amplitude information of the orthogonally transformed encoded data is reduced.

In the second embodiment of the present invention, the quantizer 120 switches the quantization parameter according to the coding control information supplied via the line 214.

The coded data whose frequency redundancy has been reduced by the information source coding unit 1 is supplied to a variable length coder 2 (see FIG. 2) via a line 101.

The block synchronization signal generated by the blocking circuit 100 is also supplied to the variable length encoder 2 (see FIG. 2) via the line 102.

FIG. 8 is a diagram showing the details of the configuration of the variable length encoder 2 according to the second embodiment of the present invention. Referring to FIG. 8, the variable-length encoder 2 includes a variable-length encoding unit 21, an escape counter 22, and a register 23. The variable-length encoding unit 21 includes a code table 210.
And a barrel shifter 250.

The encoded data output from the information source encoding unit 1 is supplied to a code table 210 via a line 101. The block synchronization signal generated by the information source coding unit 1 is supplied to an escape counter 22 and a register 23 via a line 102.

The code table 210 statistically examines the probability of occurrence of coded data whose frequency redundancy has been reduced by orthogonal transformation based on various kinds of moving picture signals. A short code is assigned, a long code is assigned to encoded data having a low occurrence frequency, and a variable-length code conversion table of encoded data as shown in Table 1 is created and prepared in advance.

When converting encoded data into a variable-length code, if the code is converted into a long code having a low frequency of occurrence as shown in Table 1, an escape signal 2
11 is output as "1".

The variable length code generated by the code table 210 is supplied to a barrel shifter 250 via a line 2125.

The escape signal generated in the code table 210 is supplied to the escape counter 22 via a line 211.

FIG. 9 is a timing chart for explaining the operation of the escape counter according to the second embodiment of the present invention.

Referring to FIG. 9, in the second embodiment of the present invention, when the escape signal is "1", the escape counter 22 updates the value of the counter, and when the escape signal is "0", Holds the count value. When the count value becomes equal to or larger than a predetermined value n, information for coarsely quantizing is output as encoding control information in order to reduce the amount of encoded information.

Referring again to FIG. 8, the encoding control information generated by escape counter 22 is supplied to register 23 via line 2223.

The escape counter 22 resets the count value at the beginning of the block according to the block synchronization signal supplied via the line 102, and at the same time, sets the coding control information to a value indicating the execution of the normal coding control. return.

The register 23 stores the escape counter 22
In the timing chart shown in FIG. 10, the encoding control information supplied from the controller is held for a predetermined time based on the block synchronization signal, as shown as a register output.

The coding control information held in the register 23 is transmitted via a line 214 to the quantizer 1 of the information source coding unit 1.
20 (see FIG. 7).

Referring to FIG. 7, quantizer 120 performs quantization during a period in which the encoding control information supplied from register 23 via line 214 indicates that the encoding parameter is coarse. Roughening is performed to reduce the amount of encoded information.

Referring again to FIG. 8, the code table 21
The variable length code, output from 0, is provided to barrel shifter 250 via line 2125. Barrel shifter 250
Performs packing of the variable length code supplied from the code table 210 via the line 2125. Since the variable-length codes output from the code table 210 have various lengths, the variable-length codes are packed in, for example, 8-bit units by a barrel shifter to eliminate waste when writing to a recording medium or sending to a transmission path.

As another method (modification) of the above-described second embodiment of the present invention, the number of continuous escape signals in a block is counted, and the counted value is determined to be equal to or greater than a predetermined value n. In this case, a method of providing coding control information for performing coarse quantization to the information source coding unit 1 for a predetermined period to reduce the amount of coding information will be described.

In this method, the code table 210, the barrel shifter 250 and the register 23 shown in FIG.
The operation of counting the escape signal in the block,
When the counted value is equal to or greater than a predetermined value n, encoding control information for performing coarse quantization is changed for a predetermined time,
This is applied to the information source coding unit 1 to reduce the amount of coded information, which is the same as the method of the above embodiment.

In this method, only the operation of the escape counter 22 in FIG. 8 is different from the above-described method. Therefore, only the operation of the escape counter 22 will be described below.

Referring to FIG. 8, the escape counter 2
2 is that at the beginning of the block, the count value is reset to zero by the block synchronization signal provided via line 102. Then, the escape signal supplied from the code table 210 via the line 211 is counted.

In counting the escape signals, the escape counter 22 counts only the continuous escape signals as shown in FIG. That is, when the escape signal changes from "1" to "0", the value of the escape counter is reset to zero.

Therefore, when the escape signal continues more than a predetermined value, encoding control information for performing coarse quantization for reducing the encoding information amount is output.

[0094]

As described above, according to the present invention,
When the number of predetermined long codes exceeds a predetermined number in a block, it is recognized that the amount of generated information is rapidly increased, and the variable length codes in subsequent blocks are replaced with, for example, zero. Accordingly, an effect is obtained that it is possible to eliminate the occurrence of excessive information generated due to a local fine pattern.

Further, according to the present invention, in the above case,
Generates coding control information that performs coarse quantization, and performs source coding based on this coding control information, thereby suppressing abrupt information generation, leaving unwritten data on the recording medium or transmitting data to the transmission path. Of the encoded data can be removed, and the continuity of the encoded image can be maintained.

[Brief description of the drawings]

FIG. 1 is a diagram for describing an embodiment of the present invention.

FIG. 2 is a diagram for explaining another embodiment of the present invention.

FIG. 3 is a diagram illustrating a configuration of an information source coding unit according to an embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a variable length encoder according to one embodiment of the present invention.

FIG. 5 is a diagram illustrating an example of an operation of an escape counter according to one embodiment of the present invention.

FIG. 6 is a diagram for explaining another example of the operation of the escape counter in one embodiment of the present invention.

FIG. 7 is a diagram illustrating a configuration of an information source coding unit according to a second embodiment of the present invention.

FIG. 8 is a diagram illustrating a configuration of a variable length encoder according to a second embodiment of the present invention.

FIG. 9 is a diagram for explaining an example of an operation of an escape counter according to the second embodiment of the present invention.

FIG. 10 is a diagram for explaining the operation of a register according to a second embodiment of the present invention.

FIG. 11 is a diagram for explaining another example of the operation of the escape counter according to the second embodiment of the present invention.

FIG. 12 is a diagram for explaining conventional variable length code allocation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Information source encoding part 2 Variable length encoder 21 Variable length encoding part 22 Escape counter 100 Blocking circuit 110 Orthogonal transformer 120 Quantizer 210 Code table 240 Switch 250 Barrel shifter

Claims (8)

(57) [Claims] When compressing a moving image signal by combining information source coding and variable length coding, a screen is divided into blocks composed of a plurality of pixels, and orthogonal transformation and quantization are performed. It reduces the frequency redundancy, scans the block in a predetermined direction, and combines the run represented by the continuous number of invalid data with the amplitude value of valid data appearing next to invalid data to form one code. In the variable length coding method, a variable length code having a short code length is assigned to data having a high frequency of occurrence, and a variable length code having a long code is allocated to data having a low frequency of occurrence. Counting the number of predetermined long codes, and switching the processing of the variable length code generated by the variable length coding according to the number of long codes. Variable-length coding method for the butterflies. 2. Compression of a moving image signal by combining information source coding and variable length coding, the screen is divided into blocks each composed of a plurality of pixels, and orthogonal transformation and quantization are performed. Is scanned in a predetermined direction in the block, and a run represented by a continuous number of invalid data and an amplitude value of valid data appearing next to the invalid data are combined to form one. When performing variable-length coding as a code, a variable-length code having a short code length is assigned to data with a high frequency of occurrence, and a variable-length code with a long code length is allocated to data with a low frequency of occurrence. In the method, counting a predetermined number of long codes that occur, and instructing switching of a quantization parameter in source coding according to the number of long codes. A variable-length encoding method characterized by the following. 3. The method according to claim 1, wherein a predetermined number of long codes generated by variable-length coding is counted in units of a block composed of a plurality of pixels, and when the counted number of long codes is equal to or more than a predetermined value. 2. The variable length coding method according to claim 1, wherein the variable length code in the subsequent blocks is replaced with zero for coding. 4. The method according to claim 1, wherein a predetermined number of long codes continuously generated by the variable length coding is counted in units of a block composed of a plurality of pixels, and the number of the continuous long codes becomes equal to or more than a predetermined value. 2. The variable-length encoding method according to claim 1, wherein the variable-length code in the subsequent blocks is replaced with zero to perform variable-length encoding. 5. The method according to claim 1, wherein a predetermined number of long codes generated by variable length coding is counted in units of a block composed of a plurality of pixels, and the counted number of long codes is equal to or more than a predetermined value. 3. The variable length encoding method according to claim 2, wherein an instruction to coarsen the quantization parameter in the information source encoding is output for a predetermined period. 6. The number of predetermined long codes continuously generated by variable length coding is counted in units of a block composed of a plurality of pixels, and the number of continuous long codes becomes equal to or more than a predetermined value. 3. The variable length encoding method according to claim 2, wherein an instruction to coarsen the quantization parameter in the information source encoding is output for a predetermined period. 7. A variable-length encoding circuit for dividing an input image signal into units of a predetermined number of pixels, orthogonally transforming the input image signal, and quantizing the variable-length data, wherein a long code generated in the block is counted. When the count value exceeds a predetermined number, a means for switching a variable length code in the subsequent block to an invalid value is provided to prevent generation of excessive information. Variable length coding device. 8. A variable-length encoding circuit that blocks an input image signal into units of a predetermined number of pixels, and performs variable-length encoding on data from an information source encoding unit for orthogonally transforming and quantizing the blocks. When the generated long code is counted and the count value exceeds a predetermined number, a command is issued to coarsen the quantization in the information source coding unit for a predetermined period, and excessive information is output. A variable-length encoding device characterized in that occurrence is prevented.